DRD3 encodes the dopamine D3 receptor, a G-protein coupled receptor primarily expressed in limbic brain regions, particularly the basal ganglia and caudate nucleus 1. The receptor couples to Gi/Go proteins to inhibit adenylate cyclase and decrease intracellular cAMP levels, playing a key role in regulating neuronal signaling pathways associated with motivation, reward, and behavior. DRD3 is significantly implicated in neuropsychiatric disorders, with meta-analyses demonstrating associations between DRD3 polymorphisms and schizophrenia, particularly in Caucasian populations 23. The receptor shows strong associations with autism spectrum disorders, where the rs167771 polymorphism correlates with repetitive and stereotyped behaviors, particularly 'sameness' behaviors, and relates to striatal volume abnormalities 14. DRD3 variants also influence essential tremor risk, especially in women and patients with earlier disease onset, with particular relevance to voice tremor 5. Additionally, DRD3 polymorphisms affect drug responses, including ADHD medication efficacy 6, risperidone-induced side effects in autism, and levodopa-associated gastrointestinal symptoms in Parkinson's disease 7. These findings highlight DRD3's crucial role in dopaminergic neurotransmission and its clinical significance in various neuropsychiatric conditions.